1. Field of the Invention
The present invention relates to a steering wheel used, for example, for an automobile and a boat, and a heater unit used for heating a wheel portion of the steering wheel. In particular, the present invention relates to the heater unit and the steering wheel that does not give discomfort to a user when operating the steering wheel.
2. Description of the Related Art
Conventionally, it is proposed that the heater unit is installed on the wheel portion of the steering wheel to warm hands of a driver in a cold condition. As shown in FIG. 3, a steering wheel 71 includes a wheel portion 72, a spoke portion 73 and a boss portion 74. The wheel portion 72 includes a wheel core material 77 and a covering material 78 formed of a synthetic resin, a textile, a leather or the like. A heater unit 31 is installed between the wheel core material 77 and the covering material 78. The heater unit 31 is connected to a not illustrated lead wire passed through the spoke portion 73 and the boss portion 74 to receive power supply.
As the heater unit installed on the steering wheel, a cord-shaped heater arranged on a substrate in a predetermined pattern shape shown in Patent documents 1 and 2 is known. Here, various foamed resin sheets, foamed rubber sheets, rubber sheets, nonwoven fabrics and woven fabrics are disclosed as the substrate.
[Patent document 1] Japanese Unexamined Patent Application Publication No. 2003-317905: Matsushita Electric Industrial Co., Ltd.
[Patent document 2] Japanese Unexamined Patent Application Publication No. 2011-121477: KURABE INDUSTRIAL CO., LTD.
However, in the conventional heater units such as the above described Patent documents 1 and 2, as shown in FIG. 8, a cord-shaped heater 101 is simply arranged on substrates 110, 110′. Therefore, thickness at a portion on which the cord-shaped heater 101 is arranged is thicker than other area. Consequently, a user feels uneven thickness when gripping the steering wheel and feels uncomfortable when operating the steering wheel.